ruby/lib/debug.rb

# Copyright (C) 2000  Network Applied Communication Laboratory, Inc.
# Copyright (C) 2000  Information-technology Promotion Agency, Japan
# Copyright (C) 2000-2003  NAKAMURA, Hiroshi  <nahi@ruby-lang.org>

require 'continuation'

if $SAFE > 0
  STDERR.print "-r debug.rb is not available in safe mode\n"
  exit 1
end

require 'tracer'
require 'pp'

class Tracer # :nodoc:
  def Tracer.trace_func(*vars)
    Single.trace_func(*vars)
  end
end

SCRIPT_LINES__ = {} unless defined? SCRIPT_LINES__ # :nodoc:

##
# This library provides debugging functionality to Ruby.
#
# To add a debugger to your code, start by requiring +debug+ in your
# program:
#
#   def say(word)
#     require 'debug'
#     puts word
#   end
#
# This will cause Ruby to interrupt execution and show a prompt when the +say+
# method is run.
#
# Once you're inside the prompt, you can start debugging your program.
#
#   (rdb:1) p word
#   "hello"
#
# == Getting help
#
# You can get help at any time by pressing +h+.
#
#   (rdb:1) h
#   Debugger help v.-0.002b
#   Commands
#     b[reak] [file:|class:]<line|method>
#     b[reak] [class.]<line|method>
#                                set breakpoint to some position
#     wat[ch] <expression>       set watchpoint to some expression
#     cat[ch] (<exception>|off)  set catchpoint to an exception
#     b[reak]                    list breakpoints
#     cat[ch]                    show catchpoint
#     del[ete][ nnn]             delete some or all breakpoints
#     disp[lay] <expression>     add expression into display expression list
#     undisp[lay][ nnn]          delete one particular or all display expressions
#     c[ont]                     run until program ends or hit breakpoint
#     s[tep][ nnn]               step (into methods) one line or till line nnn
#     n[ext][ nnn]               go over one line or till line nnn
#     w[here]                    display frames
#     f[rame]                    alias for where
#     l[ist][ (-|nn-mm)]         list program, - lists backwards
#                                nn-mm lists given lines
#     up[ nn]                    move to higher frame
#     down[ nn]                  move to lower frame
#     fin[ish]                   return to outer frame
#     tr[ace] (on|off)           set trace mode of current thread
#     tr[ace] (on|off) all       set trace mode of all threads
#     q[uit]                     exit from debugger
#     v[ar] g[lobal]             show global variables
#     v[ar] l[ocal]              show local variables
#     v[ar] i[nstance] <object>  show instance variables of object
#     v[ar] c[onst] <object>     show constants of object
#     m[ethod] i[nstance] <obj>  show methods of object
#     m[ethod] <class|module>    show instance methods of class or module
#     th[read] l[ist]            list all threads
#     th[read] c[ur[rent]]       show current thread
#     th[read] [sw[itch]] <nnn>  switch thread context to nnn
#     th[read] stop <nnn>        stop thread nnn
#     th[read] resume <nnn>      resume thread nnn
#     p expression               evaluate expression and print its value
#     h[elp]                     print this help
#     <everything else>          evaluate
#
# == Usage
#
# The following is a list of common functionalities that the debugger
# provides.
#
# === Navigating through your code
#
# In general, a debugger is used to find bugs in your program, which
# often means pausing execution and inspecting variables at some point
# in time.
#
# Let's look at an example:
#
#   def my_method(foo)
#     require 'debug'
#     foo = get_foo if foo.nil?
#     raise if foo.nil?
#   end
#
# When you run this program, the debugger will kick in just before the
# +foo+ assignment.
#
#   (rdb:1) p foo
#   nil
#
# In this example, it'd be interesting to move to the next line and
# inspect the value of +foo+ again. You can do that by pressing +n+:
#
#   (rdb:1) n # goes to next line
#   (rdb:1) p foo
#   nil
#
# You now know that the original value of +foo+ was nil, and that it
# still was nil after calling +get_foo+.
#
# Other useful commands for navigating through your code are:
#
# +c+::
#   Runs the program until it either exists or encounters another breakpoint.
#   You usually press +c+ when you are finished debugging your program and
#   want to resume its execution.
# +s+::
#   Steps into method definition. In the previous example, +s+ would take you
#   inside the method definition of +get_foo+.
# +r+::
#   Restart the program.
# +q+::
#   Quit the program.
#
# === Inspecting variables
#
# You can use the debugger to easily inspect both local and global variables.
# We've seen how to inspect local variables before:
#
#   (rdb:1) p my_arg
#   42
#
# You can also pretty print the result of variables or expressions:
#
#   (rdb:1) pp %w{a very long long array containing many words}
#   ["a",
#    "very",
#    "long",
#    ...
#   ]
#
# You can list all local variables with +v l+:
#
#   (rdb:1) v l
#     foo => "hello"
#
# Similarly, you can show all global variables with +v g+:
#
#   (rdb:1) v g
#     all global variables
#
# Finally, you can omit +p+ if you simply want to evaluate a variable or
# expression
#
#   (rdb:1) 5**2
#   25
#
# === Going beyond basics
#
# Ruby Debug provides more advanced functionalities like switching
# between threads, setting breakpoints and watch expressions, and more.
# The full list of commands is available at any time by pressing +h+.
#
# == Staying out of trouble
#
# Make sure you remove every instance of +require 'debug'+ before
# shipping your code. Failing to do so may result in your program
# hanging unpredictably.
#
# Debug is not available in safe mode.

class DEBUGGER__
  MUTEX = Mutex.new # :nodoc:

  class Context # :nodoc:
    DEBUG_LAST_CMD = []

    begin
      require 'readline'
      def readline(prompt, hist)
        Readline::readline(prompt, hist)
      end
    rescue LoadError
      def readline(prompt, hist)
        STDOUT.print prompt
        STDOUT.flush
        line = STDIN.gets
        exit unless line
        line.chomp!
        line
      end
      USE_READLINE = false
    end

    def initialize
      if Thread.current == Thread.main
        @stop_next = 1
      else
        @stop_next = 0
      end
      @last_file = nil
      @file = nil
      @line = nil
      @no_step = nil
      @frames = []
      @finish_pos = 0
      @trace = false
      @catch = "StandardError"
      @suspend_next = false
    end

    def stop_next(n=1)
      @stop_next = n
    end

    def set_suspend
      @suspend_next = true
    end

    def clear_suspend
      @suspend_next = false
    end

    def suspend_all
      DEBUGGER__.suspend
    end

    def resume_all
      DEBUGGER__.resume
    end

    def check_suspend
      while MUTEX.synchronize {
          if @suspend_next
            DEBUGGER__.waiting.push Thread.current
            @suspend_next = false
            true
          end
        }
      end
    end

    def trace?
      @trace
    end

    def set_trace(arg)
      @trace = arg
    end

    def stdout
      DEBUGGER__.stdout
    end

    def break_points
      DEBUGGER__.break_points
    end

    def display
      DEBUGGER__.display
    end

    def context(th)
      DEBUGGER__.context(th)
    end

    def set_trace_all(arg)
      DEBUGGER__.set_trace(arg)
    end

    def set_last_thread(th)
      DEBUGGER__.set_last_thread(th)
    end

    def debug_eval(str, binding)
      begin
        eval(str, binding)
      rescue StandardError, ScriptError => e
        at = eval("caller(1)", binding)
        stdout.printf "%s:%s\n", at.shift, e.to_s.sub(/\(eval\):1:(in `.*?':)?/, '')
        for i in at
          stdout.printf "\tfrom %s\n", i
        end
        throw :debug_error
      end
    end

    def debug_silent_eval(str, binding)
      begin
        eval(str, binding)
      rescue StandardError, ScriptError
        nil
      end
    end

    def var_list(ary, binding)
      ary.sort!
      for v in ary
        stdout.printf "  %s => %s\n", v, eval(v.to_s, binding).inspect
      end
    end

    def debug_variable_info(input, binding)
      case input
      when /^\s*g(?:lobal)?\s*$/
        var_list(global_variables, binding)

      when /^\s*l(?:ocal)?\s*$/
        var_list(eval("local_variables", binding), binding)

      when /^\s*i(?:nstance)?\s+/
        obj = debug_eval($', binding)
        var_list(obj.instance_variables, obj.instance_eval{binding()})

      when /^\s*c(?:onst(?:ant)?)?\s+/
        obj = debug_eval($', binding)
        unless obj.kind_of? Module
          stdout.print "Should be Class/Module: ", $', "\n"
        else
          var_list(obj.constants, obj.module_eval{binding()})
        end
      end
    end

    def debug_method_info(input, binding)
      case input
      when /^i(:?nstance)?\s+/
        obj = debug_eval($', binding)

        len = 0
        for v in obj.methods.sort
          len += v.size + 1
          if len > 70
            len = v.size + 1
            stdout.print "\n"
          end
          stdout.print v, " "
        end
        stdout.print "\n"

      else
        obj = debug_eval(input, binding)
        unless obj.kind_of? Module
          stdout.print "Should be Class/Module: ", input, "\n"
        else
          len = 0
          for v in obj.instance_methods(false).sort
            len += v.size + 1
            if len > 70
              len = v.size + 1
              stdout.print "\n"
            end
            stdout.print v, " "
          end
          stdout.print "\n"
        end
      end
    end

    def thnum
      num = DEBUGGER__.instance_eval{@thread_list[Thread.current]}
      unless num
        DEBUGGER__.make_thread_list
        num = DEBUGGER__.instance_eval{@thread_list[Thread.current]}
      end
      num
    end

    def debug_command(file, line, id, binding)
      MUTEX.lock
      unless defined?($debugger_restart) and $debugger_restart
        callcc{|c| $debugger_restart = c}
      end
      set_last_thread(Thread.current)
      frame_pos = 0
      binding_file = file
      binding_line = line
      previous_line = nil
      if ENV['EMACS']
        stdout.printf "\032\032%s:%d:\n", binding_file, binding_line
      else
        stdout.printf "%s:%d:%s", binding_file, binding_line,
          line_at(binding_file, binding_line)
      end
      @frames[0] = [binding, file, line, id]
      display_expressions(binding)
      prompt = true
      while prompt and input = readline("(rdb:%d) "%thnum(), true)
        catch(:debug_error) do
          if input == ""
            next unless DEBUG_LAST_CMD[0]
            input = DEBUG_LAST_CMD[0]
            stdout.print input, "\n"
          else
            DEBUG_LAST_CMD[0] = input
          end

          case input
          when /^\s*tr(?:ace)?(?:\s+(on|off))?(?:\s+(all))?$/
            if defined?( $2 )
              if $1 == 'on'
                set_trace_all true
              else
                set_trace_all false
              end
            elsif defined?( $1 )
              if $1 == 'on'
                set_trace true
              else
                set_trace false
              end
            end
            if trace?
              stdout.print "Trace on.\n"
            else
              stdout.print "Trace off.\n"
            end

          when /^\s*b(?:reak)?\s+(?:(.+):)?([^.:]+)$/
            pos = $2
            if $1
              klass = debug_silent_eval($1, binding)
              file = $1
            end
            if pos =~ /^\d+$/
              pname = pos
              pos = pos.to_i
            else
              pname = pos = pos.intern.id2name
            end
            break_points.push [true, 0, klass || file, pos]
            stdout.printf "Set breakpoint %d at %s:%s\n", break_points.size, klass || file, pname

          when /^\s*b(?:reak)?\s+(.+)[#.]([^.:]+)$/
            pos = $2.intern.id2name
            klass = debug_eval($1, binding)
            break_points.push [true, 0, klass, pos]
            stdout.printf "Set breakpoint %d at %s.%s\n", break_points.size, klass, pos

          when /^\s*wat(?:ch)?\s+(.+)$/
            exp = $1
            break_points.push [true, 1, exp]
            stdout.printf "Set watchpoint %d:%s\n", break_points.size, exp

          when /^\s*b(?:reak)?$/
            if break_points.find{|b| b[1] == 0}
              n = 1
              stdout.print "Breakpoints:\n"
              break_points.each do |b|
                if b[0] and b[1] == 0
                  stdout.printf "  %d %s:%s\n", n, b[2], b[3]
                end
                n += 1
              end
            end
            if break_points.find{|b| b[1] == 1}
              n = 1
              stdout.print "\n"
              stdout.print "Watchpoints:\n"
              for b in break_points
                if b[0] and b[1] == 1
                  stdout.printf "  %d %s\n", n, b[2]
                end
                n += 1
              end
            end
            if break_points.size == 0
              stdout.print "No breakpoints\n"
            else
              stdout.print "\n"
            end

          when /^\s*del(?:ete)?(?:\s+(\d+))?$/
            pos = $1
            unless pos
              input = readline("Clear all breakpoints? (y/n) ", false)
              if input == "y"
                for b in break_points
                  b[0] = false
                end
              end
            else
              pos = pos.to_i
              if break_points[pos-1]
                break_points[pos-1][0] = false
              else
                stdout.printf "Breakpoint %d is not defined\n", pos
              end
            end

          when /^\s*disp(?:lay)?\s+(.+)$/
            exp = $1
            display.push [true, exp]
            stdout.printf "%d: ", display.size
            display_expression(exp, binding)

          when /^\s*disp(?:lay)?$/
            display_expressions(binding)

          when /^\s*undisp(?:lay)?(?:\s+(\d+))?$/
            pos = $1
            unless pos
              input = readline("Clear all expressions? (y/n) ", false)
              if input == "y"
                for d in display
                  d[0] = false
                end
              end
            else
              pos = pos.to_i
              if display[pos-1]
                display[pos-1][0] = false
              else
                stdout.printf "Display expression %d is not defined\n", pos
              end
            end

          when /^\s*c(?:ont)?$/
            prompt = false

          when /^\s*s(?:tep)?(?:\s+(\d+))?$/
            if $1
              lev = $1.to_i
            else
              lev = 1
            end
            @stop_next = lev
            prompt = false

          when /^\s*n(?:ext)?(?:\s+(\d+))?$/
            if $1
              lev = $1.to_i
            else
              lev = 1
            end
            @stop_next = lev
            @no_step = @frames.size - frame_pos
            prompt = false

          when /^\s*w(?:here)?$/, /^\s*f(?:rame)?$/
            display_frames(frame_pos)

          when /^\s*l(?:ist)?(?:\s+(.+))?$/
            if not $1
              b = previous_line ? previous_line + 10 : binding_line - 5
              e = b + 9
            elsif $1 == '-'
              b = previous_line ? previous_line - 10 : binding_line - 5
              e = b + 9
            else
              b, e = $1.split(/[-,]/)
              if e
                b = b.to_i
                e = e.to_i
              else
                b = b.to_i - 5
                e = b + 9
              end
            end
            previous_line = b
            display_list(b, e, binding_file, binding_line)

          when /^\s*up(?:\s+(\d+))?$/
            previous_line = nil
            if $1
              lev = $1.to_i
            else
              lev = 1
            end
            frame_pos += lev
            if frame_pos >= @frames.size
              frame_pos = @frames.size - 1
              stdout.print "At toplevel\n"
            end
            binding, binding_file, binding_line = @frames[frame_pos]
            stdout.print format_frame(frame_pos)

          when /^\s*down(?:\s+(\d+))?$/
            previous_line = nil
            if $1
              lev = $1.to_i
            else
              lev = 1
            end
            frame_pos -= lev
            if frame_pos < 0
              frame_pos = 0
              stdout.print "At stack bottom\n"
            end
            binding, binding_file, binding_line = @frames[frame_pos]
            stdout.print format_frame(frame_pos)

          when /^\s*fin(?:ish)?$/
            if frame_pos == @frames.size
              stdout.print "\"finish\" not meaningful in the outermost frame.\n"
            else
              @finish_pos = @frames.size - frame_pos
              frame_pos = 0
              prompt = false
            end

          when /^\s*cat(?:ch)?(?:\s+(.+))?$/
            if $1
              excn = $1
              if excn == 'off'
                @catch = nil
                stdout.print "Clear catchpoint.\n"
              else
                @catch = excn
                stdout.printf "Set catchpoint %s.\n", @catch
              end
            else
              if @catch
                stdout.printf "Catchpoint %s.\n", @catch
              else
                stdout.print "No catchpoint.\n"
              end
            end

          when /^\s*q(?:uit)?$/
            input = readline("Really quit? (y/n) ", false)
            if input == "y"
              exit!  # exit -> exit!: No graceful way to stop threads...
            end

          when /^\s*v(?:ar)?\s+/
            debug_variable_info($', binding)

          when /^\s*m(?:ethod)?\s+/
            debug_method_info($', binding)

          when /^\s*th(?:read)?\s+/
            if DEBUGGER__.debug_thread_info($', binding) == :cont
              prompt = false
            end

          when /^\s*pp\s+/
            PP.pp(debug_eval($', binding), stdout)

          when /^\s*p\s+/
            stdout.printf "%s\n", debug_eval($', binding).inspect

          when /^\s*r(?:estart)?$/
            $debugger_restart.call

          when /^\s*h(?:elp)?$/
            debug_print_help()

          else
            v = debug_eval(input, binding)
            stdout.printf "%s\n", v.inspect
          end
        end
      end
      MUTEX.unlock
      resume_all
    end

    def debug_print_help
      stdout.print <<EOHELP
Debugger help v.-0.002b
Commands
  b[reak] [file:|class:]<line|method>
  b[reak] [class.]<line|method>
                             set breakpoint to some position
  wat[ch] <expression>       set watchpoint to some expression
  cat[ch] (<exception>|off)  set catchpoint to an exception
  b[reak]                    list breakpoints
  cat[ch]                    show catchpoint
  del[ete][ nnn]             delete some or all breakpoints
  disp[lay] <expression>     add expression into display expression list
  undisp[lay][ nnn]          delete one particular or all display expressions
  c[ont]                     run until program ends or hit breakpoint
  s[tep][ nnn]               step (into methods) one line or till line nnn
  n[ext][ nnn]               go over one line or till line nnn
  w[here]                    display frames
  f[rame]                    alias for where
  l[ist][ (-|nn-mm)]         list program, - lists backwards
                             nn-mm lists given lines
  up[ nn]                    move to higher frame
  down[ nn]                  move to lower frame
  fin[ish]                   return to outer frame
  tr[ace] (on|off)           set trace mode of current thread
  tr[ace] (on|off) all       set trace mode of all threads
  q[uit]                     exit from debugger
  v[ar] g[lobal]             show global variables
  v[ar] l[ocal]              show local variables
  v[ar] i[nstance] <object>  show instance variables of object
  v[ar] c[onst] <object>     show constants of object
  m[ethod] i[nstance] <obj>  show methods of object
  m[ethod] <class|module>    show instance methods of class or module
  th[read] l[ist]            list all threads
  th[read] c[ur[rent]]       show current thread
  th[read] [sw[itch]] <nnn>  switch thread context to nnn
  th[read] stop <nnn>        stop thread nnn
  th[read] resume <nnn>      resume thread nnn
  pp expression              evaluate expression and pretty_print its value
  p expression               evaluate expression and print its value
  r[estart]                  restart program
  h[elp]                     print this help
  <everything else>          evaluate
EOHELP
    end

    def display_expressions(binding)
      n = 1
      for d in display
        if d[0]
          stdout.printf "%d: ", n
          display_expression(d[1], binding)
        end
        n += 1
      end
    end

    def display_expression(exp, binding)
      stdout.printf "%s = %s\n", exp, debug_silent_eval(exp, binding).to_s
    end

    def frame_set_pos(file, line)
      if @frames[0]
        @frames[0][1] = file
        @frames[0][2] = line
      end
    end

    def display_frames(pos)
      0.upto(@frames.size - 1) do |n|
        if n == pos
          stdout.print "--> "
        else
          stdout.print "    "
        end
        stdout.print format_frame(n)
      end
    end

    def format_frame(pos)
      _, file, line, id = @frames[pos]
      sprintf "#%d %s:%s%s\n", pos + 1, file, line,
        (id ? ":in `#{id.id2name}'" : "")
    end

    def script_lines(file, line)
      unless (lines = SCRIPT_LINES__[file]) and lines != true
        Tracer::Single.get_line(file, line) if File.exist?(file)
        lines = SCRIPT_LINES__[file]
        lines = nil if lines == true
      end
      lines
    end

    def display_list(b, e, file, line)
      if lines = script_lines(file, line)
        stdout.printf "[%d, %d] in %s\n", b, e, file
        b.upto(e) do |n|
          if n > 0 && lines[n-1]
            if n == line
              stdout.printf "=> %d  %s\n", n, lines[n-1].chomp
            else
              stdout.printf "   %d  %s\n", n, lines[n-1].chomp
            end
          end
        end
      else
        stdout.printf "No sourcefile available for %s\n", file
      end
    end

    def line_at(file, line)
      lines = script_lines(file, line)
      if lines and line = lines[line-1]
        return line
      end
      return "\n"
    end

    def debug_funcname(id)
      if id.nil?
        "toplevel"
      else
        id.id2name
      end
    end

    def check_break_points(file, klass, pos, binding, id)
      return false if break_points.empty?
      n = 1
      for b in break_points
        if b[0]           # valid
          if b[1] == 0    # breakpoint
            if (b[2] == file and b[3] == pos) or
                (klass and b[2] == klass and b[3] == pos)
              stdout.printf "Breakpoint %d, %s at %s:%s\n", n, debug_funcname(id), file, pos
              return true
            end
          elsif b[1] == 1 # watchpoint
            if debug_silent_eval(b[2], binding)
              stdout.printf "Watchpoint %d, %s at %s:%s\n", n, debug_funcname(id), file, pos
              return true
            end
          end
        end
        n += 1
      end
      return false
    end

    def excn_handle(file, line, id, binding)
      if $!.class <= SystemExit
        set_trace_func nil
        exit
      end

      if @catch and ($!.class.ancestors.find { |e| e.to_s == @catch })
        stdout.printf "%s:%d: `%s' (%s)\n", file, line, $!, $!.class
        fs = @frames.size
        tb = caller(0)[-fs..-1]
        if tb
          for i in tb
            stdout.printf "\tfrom %s\n", i
          end
        end
        suspend_all
        debug_command(file, line, id, binding)
      end
    end

    def trace_func(event, file, line, id, binding, klass)
      Tracer.trace_func(event, file, line, id, binding, klass) if trace?
      context(Thread.current).check_suspend
      @file = file
      @line = line
      case event
      when 'line'
        frame_set_pos(file, line)
        if !@no_step or @frames.size == @no_step
          @stop_next -= 1
          @stop_next = -1 if @stop_next < 0
        elsif @frames.size < @no_step
          @stop_next = 0          # break here before leaving...
        else
          # nothing to do. skipped.
        end
        if @stop_next == 0 or check_break_points(file, nil, line, binding, id)
          @no_step = nil
          suspend_all
          debug_command(file, line, id, binding)
        end

      when 'call'
        @frames.unshift [binding, file, line, id]
        if check_break_points(file, klass, id.id2name, binding, id)
          suspend_all
          debug_command(file, line, id, binding)
        end

      when 'c-call'
        frame_set_pos(file, line)

      when 'class'
        @frames.unshift [binding, file, line, id]

      when 'return', 'end'
        if @frames.size == @finish_pos
          @stop_next = 1
          @finish_pos = 0
        end
        @frames.shift

      when 'raise'
        excn_handle(file, line, id, binding)

      end
      @last_file = file
    end
  end

  trap("INT") { DEBUGGER__.interrupt }
  @last_thread = Thread::main
  @max_thread = 1
  @thread_list = {Thread::main => 1}
  @break_points = []
  @display = []
  @waiting = []
  @stdout = STDOUT

  class << DEBUGGER__
    # Returns the IO used as stdout. Defaults to STDOUT
    def stdout
      @stdout
    end

    # Sets the IO used as stdout. Defaults to STDOUT
    def stdout=(s)
      @stdout = s
    end

    # Returns the display expression list
    #
    # See DEBUGGER__ for more usage
    def display
      @display
    end

    # Returns the list of break points where execution will be stopped.
    #
    # See DEBUGGER__ for more usage
    def break_points
      @break_points
    end

    # Returns the list of waiting threads.
    #
    # When stepping through the traces of a function, thread gets suspended, to
    # be resumed later.
    def waiting
      @waiting
    end

    def set_trace( arg )
      MUTEX.synchronize do
        make_thread_list
        for th, in @thread_list
          context(th).set_trace arg
        end
      end
      arg
    end

    def set_last_thread(th)
      @last_thread = th
    end

    def suspend
      MUTEX.synchronize do
        make_thread_list
        for th, in @thread_list
          next if th == Thread.current
          context(th).set_suspend
        end
      end
      # Schedule other threads to suspend as soon as possible.
      Thread.pass
    end

    def resume
      MUTEX.synchronize do
        make_thread_list
        @thread_list.each do |th,|
          next if th == Thread.current
          context(th).clear_suspend
        end
        waiting.each do |th|
          th.run
        end
        waiting.clear
      end
      # Schedule other threads to restart as soon as possible.
      Thread.pass
    end

    def context(thread=Thread.current)
      c = thread[:__debugger_data__]
      unless c
        thread[:__debugger_data__] = c = Context.new
      end
      c
    end

    def interrupt
      context(@last_thread).stop_next
    end

    def get_thread(num)
      th = @thread_list.key(num)
      unless th
        @stdout.print "No thread ##{num}\n"
        throw :debug_error
      end
      th
    end

    def thread_list(num)
      th = get_thread(num)
      if th == Thread.current
        @stdout.print "+"
      else
        @stdout.print " "
      end
      @stdout.printf "%d ", num
      @stdout.print th.inspect, "\t"
      file = context(th).instance_eval{@file}
      if file
        @stdout.print file,":",context(th).instance_eval{@line}
      end
      @stdout.print "\n"
    end

    def thread_list_all
      for th in @thread_list.values.sort
        thread_list(th)
      end
    end

    def make_thread_list
      hash = {}
      for th in Thread::list
        if @thread_list.key? th
          hash[th] = @thread_list[th]
        else
          @max_thread += 1
          hash[th] = @max_thread
        end
      end
      @thread_list = hash
    end

    def debug_thread_info(input, binding)
      case input
      when /^l(?:ist)?/
        make_thread_list
        thread_list_all

      when /^c(?:ur(?:rent)?)?$/
        make_thread_list
        thread_list(@thread_list[Thread.current])

      when /^(?:sw(?:itch)?\s+)?(\d+)/
        make_thread_list
        th = get_thread($1.to_i)
        if th == Thread.current
          @stdout.print "It's the current thread.\n"
        else
          thread_list(@thread_list[th])
          context(th).stop_next
          th.run
          return :cont
        end

      when /^stop\s+(\d+)/
        make_thread_list
        th = get_thread($1.to_i)
        if th == Thread.current
          @stdout.print "It's the current thread.\n"
        elsif th.stop?
          @stdout.print "Already stopped.\n"
        else
          thread_list(@thread_list[th])
          context(th).suspend
        end

      when /^resume\s+(\d+)/
        make_thread_list
        th = get_thread($1.to_i)
        if th == Thread.current
          @stdout.print "It's the current thread.\n"
        elsif !th.stop?
          @stdout.print "Already running."
        else
          thread_list(@thread_list[th])
          th.run
        end
      end
    end
  end

  stdout.printf "Debug.rb\n"
  stdout.printf "Emacs support available.\n\n"
  RubyVM::InstructionSequence.compile_option = {
    trace_instruction: true
  }
  set_trace_func proc { |event, file, line, id, binding, klass, *rest|
    DEBUGGER__.context.trace_func event, file, line, id, binding, klass
  }
end